This invention relates to the modification of macromolecular species such as proteins, injectable compounds in general and solid supports, by conjugation with polymers. This invention further relates to activated polymers for use in such conjugation.
Polymers, such as polyethylene glycol, polypropylene glycol and analogs, have been coupled to enzymes, drugs, polypeptides and poly(amino acids) of various kinds to modify their immunological and biochemical properties. Among the desirable changes achieved in this manner are the reduction or elimination of immunogenicity, induction of tolerance, an increased resistance to proteolytic degradation in the serum, a controlled or gradual release (in the case of a drug) arising from a slow rate of enzyme-induced dissociation from the polymer, an alteration in the tissue distribution (in the case of a drug, for instance) by varying its water solubility or its molecular size, a change in surface characteristics (in the case of a solid support), and, in the case of an enzyme, for instance, a change in kinetics, a shift in the pH and temperature optima, and altered reactivity to substrate.
The goal of conjugation in most cases is to modify certain properties while retaining others (such as drug or enzyme activity, for instance) substantially unchanged. In many cases, this selectivity varies with the locus of the conjugation site on the macromolecule, and the number of sites on a single macromolecule which take part in the conjugation. Most conjugations to date have been made at amino moieties on drugs or enzymes. In many cases, this presents a problem due to the wide distribution of reactive amino groups on the molecule. The result is often a lack of control over the degree or rate of conjugation, and a substantial interference with the desired activity of the macromolecule. In an immunoglobulin, for instance, where the antigen-binding portions bear a large number of amino groups, conjugation at these groups can cause interference with the immunoglobulin s ability to bind antigen.